Rolling mill



A. L. KRAUSE ROLLING MILL Filed Feb. 23, 1933 Fi .I.

Fig.2

Inveht-or 1 Au ust L.Kr*ause His Attorneg Patented May 4, 1937 PATENT 'O'IFFICE ROLLING MILL August L. Krause, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York pplication February '23, 1933, Serial No. 658,003

16 Claims.

This invention relates to rolling mills, more particularly to systems for controlling, the operation thereof, and it has for an object the provision of a simple, reliable and efficient means for exerting a braking torque on the mill and preventing back lash in the mill driving connections.

A more specific object of the invention is the provision of a system of the above character in which the energy producing thebraking torque is returned to the system and in which the torque is maintained substantially constant, irrespective of variations in the mill speed and without utilizing any external control devices.

In carrying the invention into effect in one formthereof, the mill is driven by a suitable driving means, and a generator driven by the mill is electrically connected to a motor that is mechanically connected to the main driving motor so that the torque exerted by the generator on the mill is maintained substantially constant 'irre spective of variations in the mill speed, and the energy producing the braking torque is recovered and returned to the system.

In illustrating the invention in one form thereof, it is shown as applied to a rolling mill in which a plurality of mill elements are driven from a single shaft and the mill motor is connected to the shaft at a point intermediate the several mill elements. It will be understood, however, that the invention is equally. applicable to a mill in which the driving motor is connected to an extremity of the main drive shaft.

For a better and more complete understanding of the invention reference should now be had to the following specification and to the accompanying drawing in which Fig. 1 is a simple diagrammatical representation of an embodiment of the invention and Fig. 2 is a simple diagrammatical representation of a modification.

Referring now to the drawing, a plurality of inill elements In, I, and I2 and a second plurality of mill elements |3, l4, and I5 are connected to a suitable driving shaft it. The first group of mill elements In, H, and I2 are arranged at one extremity of the shaft while the second group l3, l4, |5 are arranged at the opposite extremity thereof. Suitable couplings (not shown) are usually provided between each mill element and the adjacent element. These couplings usually have a certain amount of back lash that is undesirable in the operation of themill.

The driving shaft |5 is driven by any suitable driving means such for example as that represented by the electric motor I! to the drive shaft of which the mill driving shaft I6 is connected by suitable speed reduction gearing l8.

The motor I! may be of any suitable type, but it is preferably of a type that is subject to some variation in its speed with increasing load so that flywheels 20 may be provided for storing energy at certain intervals of the operation and giving upenergy to the system as the load increases.

The gearing l8 usually contains a certain amount of back lash which like the back lash in the driving coupling is undesirable in the operation of the system because of the shocks resulting to the apparatus upon variation in the speed of the mill.

In order to prevent the shocks resulting to the apparatus from the presence of back lash in the driving connections, means are provided for exerting a braking torque on the mill. These means are illustrated as a pair of direct current generators 2| and 22 and a direct current motor 23. As shown, the armature of the direct current generator 2| is mechanically connected to an extremity of the mill drive shaft |6 by means of suitable gearing 24, whilst the direct current generator 22 is mechanically coupled to the opposite extremity of the shaft I6 by means of suitable gearing 25. As shown, the generators 2| and 22 are respectively provided with direct current field windings 26 and 21 which in turn are supplied with direct current from any suitable source such for example as that represented in the drawing by the two supply lines 28. Variable resistances 30 and 3| are respectively included in the connections between the field windings 26 and 21 and the supply source 28. These resistances serve to adjust the excitation of the generators to any desired values. It will be understood that when the generators 2| and 22 are driven by the mill shaft l6 and have their armatures connected to a suitable load circuit, the braking torque is exerted on the drive shaft l6 and this torque takes up the back lash in the gearing and other couplings present in the mill. The generators 2| and 22 therefore serve as drag generators to produce a back torque on the mill shaft.

In order to exert a back torque, it is necessary that a certain amount of energy be taken from the shaft l6 and transmitted through the generators 2| and 22. By controlling the amount of this energy, the magnitude of the torque itself can be controlled. For this purpose the armature of the generators 2| and 22 are connected to the armature of the motor 23. illustrated as a direct current motor and is pro- Motor 23 is vided with a direct current field winding 23.; which in turn is supplied with direct current from the source 28, to which it is connected, as shown, with a variable resistance 32 included in the connections for varying the excitation and consequently the countervoltage of the motor. Adjustment of the resistances 30, 3| and 32 serves to adjust the braking torque of the drag generators to any desired value.

The motor 23 thus serves as a load for the drag generators 2| and 22 and in order that the energy transmitted from these generators to the motor 23 shall not be wasted, the armature of the motor 23 is mechanically connected to the drive shaft of the main driving motor l1 so that any energy.

received from the generators in electrical form is converted into the form of mechanical energy and thus returned to the system.

The shocks resulting to the rolling mill apparatus'due to-back lash in the gearing and other driving connections are particularly prevalent and disastrous when the speed of the mill changes suddenly due to a change in the load or a change in the distribution of the load. However, by maintaining the torque exerted by the drag generators 2| and 22 substantially constant, back lash and resultant apparatus shocks are efiectlvely eliminated.

In operation, the switches 33 and 34 are operated to their closed positions. The main mill motor I! is started and brought up to speed in a manner that is well understood in the art. Rotation of the main mill shaft I6 of course effects rotation of the armatures of the drag generators 2| and 22 so that the latter pump energy to the auxiliary motor 23 and as a result exert .a back torque on the shaft I6 due to the energy thus transmitted.

Assume now that the distribution of load on the main'mill shaft l6 suddenly changes, 1. e. the load is increased on stand l3. This increase in load naturally tends to slow down the shaft l6.

Due, however, to the inertias of stands l4 and I5 back lash tends to arise in the couplings between stands l3 and I4 and stands l4 and I5. This tendency, however, is overcome by the braking torque exerted on the shaft by the drag generator 22.

Furthermore, this back torque is maintained substantially constant irrespectively of changes in the speed of the mill. If the speed of the mill is decreased, the speed of rotation and the generated voltage of the drag generators 2| and 22 likewise decreases and consequently there is a tendency for the output current supplied from the generators 2| and 22 to the motor 23 to decrease. A reduction in the current supplied by the generators 2| and 22 would of course mean a decrease in the back torque exerted on the shaft I6. However, as the speed of the drive shaft l6 decreases due to the increasing load, the speed of the motor 23 is likewise decreased since as previously pointed out, its armature member is mechanically connected to the driving shaft of the main driving motor l1 and consequently through the gearing ll 8 to the mill shaft I5. The decrease in the speed of the motor 23 efiects a decrease in its counter voltage which compensates for the tendency of the current supplied by the generators 2| and 22 to decrease. That is to say, the counter voltage of themotor 23 rises and fallswith increases and decreases in the generated voltage of the drag generators 2| and 22 so that the net result is to maintain'a substantially constant current supply from on which the main motor is somewhat overloaded.

In the modified system of Fig. 2 the mill elements 35 to 4| and the main driving motor 42- are in all respects similar to the corresponding element of Fig. 1. However, the drag generators 43 and 44 are illustrated as alternating current induction machines. Preferably these induction machines 43 and 44 are in the form of wound rotor induction motors having predetermined amounts of resistance 45 and 46 respectively connected in their secondary circuits as illustrated. The auxiliary machine 41 is also an alternating current dynamo electric machine and is preferably in the nature of a synchronous machine, having a direct current field winding (not shown) supplied with direct current from any suitable source such as that represented by the two supply lines 48 to which the field winding is connected through slip rings 49. The armature of the auxiliary machine 41 is mechanically connected to the drive shaft of the main driving motor 42 and is consequently connected to the main mill driving shaft 50 through the gearing 5|.

' 53 respectively. The ratios of the gearings 52 and 53 are so chosen that the drag generators 43 and 44 are driven at a speed that is slightly above synchronism with respect to the auxiliary machine 41. When an induction machine is driven above synchronous speed, it acts as an induction generator, and it will thus be seen that when the switches 54 and 55 are closed to connect the armature connections of the induction machines 43 and 44 to the armature of the auxiliary machine 41, the induction machines 43 and 44 act as drag generators pumping energy to the auxiliary machine 41 and thereby exerting a back torque on the main mill shaft 50.

The secondary resistances 45 and 46 are ini tially proportioned so that the magnitude of the current. supplied by the induction machines 43 and 44 to the auxiliary machine 41 has a desired predetermined value.

. In operation, the manually operated switches 1 54 and 55 are moved to their closed position. The

mill is started and brought to speed in the usual manner. Increases and decreases in the load on the mill produce correspondingincreases and decreases in the speed of the main mill-shaft 50 and likewise in the speed of the induction machines 43 and 44 and the synchronous auxiliary machine 41. As the speed of the complete mill equipment rises and falls, the induction machines 43 and 44 and the auxiliary machine 41 are sub ject to corresponding changes in the speed resulting in approximately a constant torque at the dragging end of "the mill.

Thusit will be seen that the invention malntains a substantially constant back torque on the main mill shaft and apparatus and thereby pre- An advantage of the invention is that after the original set up is made, the system is inherently self-regulating insofar as maintaining a substantially constant dragging torque and does not require the help of any external regulating apparatus.

If the. mill is arranged with the driving motor at one end of the main mill shaft instead of connected to the central position illustrated in the drawing, only one drag generator at the opposite end of the shaft is necessary.

Although in accordance with the provisions of the patent, statutes the invention is described as embodied in concrete form, it will'be understood that the elements, apparatus and connections shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a rolling mill provided with a plurality of rolls, driving means connected to said mill at one end of the rolls thereof, a dynamo electric machine connected to said mill at the opposite end of the rolls for exerting a braking torque to prevent back lash, and a second dynamo electric machine mechanically connected to said driving means and connected to said first dynamo electric machine.

.2. In combination, a rolling mill, an electric motor for'driving said mill, an electric generator driven by said mill for exerting a. braking torque thereon to prevent back lash, and an auxiliary motor mounted on the shaft of said driving motor and electrically connected to said generator for maintaining said braking torque substantially constant with variations in the speed of said mill.

3. A control system for a rolling mill comprising an electric motor subject to speed variation connected to the mill shaft at one end of the mill rolls for driving the mill, a. direct current generator connected to the mill shaft at the opposite end of the rolls so as to be driven through the mill for exerting a braking torque thereon to preventback lash in the driving connect-ions and couplings, and a direct current motor mechanically connected to said driving motor and electrically. connected to said generator for returning the energy required to torque to the system.

4. In' combination with a rolling mill, having a produce said braking plurality of elements connected to a common shaft, an electric motor connected to drive said shaft at a point between said elements, a pair ofdirect currentgenerators connected to opposite extremities of said shaft for exerting a braking torque on said mill elements to prevent back lash in the driving connections, and a direct ourr rent motor mechanically connected to said driving motor and electrically connected to said generators thereby to maintain the current from said generators to said direct current motor substantially constant irrespective of changes in the speed of said mill.

5.'In combination with a rolling mill, an electric motor for driving said mill, an alternating current machine driven by the mill for exerting a braking'torque thereon to prevent back lash in the driving connections and an auxiliary alternating current machine directly connected to the drive shaft of said driving motor and electrically connected to said first mentioned alternating curerator and auxiliary motor to vary duction machine above synchronous speed so as to exert a braking torque on said mill and prevent back lash in the driving connections.

7. The combination with a work machine having a train of work elements and a main motor for driving the work machine, of a synchronous motor mechanically connected to the main motor, an induction generator connected to the end of the train of work elements, means for electrically connecting the motor to receive power from the generator, and means for varying the excitation of the motor to control the braking torque exerted on the machine by the induction generator.

8. In combination with a work machine having a plurality of work elements and driving connections between said elements, driving means provided with a drive shaft connected to drive said elements, a dynamo-electric machine connected to said work elements to be driven thereby, a second dynamo-electric machine electrically connected to receive power from said first dynamoelectric machine and having its shaft connected to said drive shaft independently of said driving connections thereby to provide for exerting a braking torque on said work machine to prevent back-lash and to utilize the braking energy to drive said machine.

9. In combination with a rolling 'mill and the like having a train of roll stands for performing operations upon a material, amain motor having its drive shaft connected to one end of said train to drive said mill, a drag generator connected to said mill at the opposite end of said train of rolls to be driven thereby for exerting a braking torque to prevent back-lash, an auxiliary motor electrically connected to receive power from said generator, and a driving connection between said auxiliary motor and main motor independent of said material to provide for utilization of the braking energy to drive said mill and to vary the counter-voltage of said auxiliary motor with the speed of said mill thereby to maintain, said braking torque substantially constant with varying mill speed. v

10. In combination with a machine having a train of work performing elements and driving connections between said elements, a main motor having its shaft connected to one end of said train to drive said elements, a generator connected to the opposite end of said train and driven thereby, an auxiliary motor electrically connected to receive power from said generator thereby to provide a braking torque on said mill to preventback-lash in said driving connections, said auxiliary motor having its shaft connected to the drive shaft of said main motor independently of said driving connections, thereby to utilize the braking energy to drive said mill, and means for varying the power transmitted between said gensaid braking torque. k I

11. The combination with a rolling mill and the like having a train of work elements and driving connections between said elements, of a main (6 motor having its shaft connected to one end of said train for driving said mill, an alternating current generator connected to the opposite end of said train and driven thereby, and an alternating current motor electrically connected to receive power from said generator to provide a braking torque on the mill to prevent back-lash,

said alternating current motor having its shaft power from the induction generator, thereby.

to provide for subjecting the mill to a braking torque and converting the braking energy into electrical energy to drive the mill.

13. The combination with a rolling mill and the like having a train of work elements, and a main motor connected to one end of said train for driving the mill, of a synchronous motorhaving its shaft connected to the shaft of said main motor at said end of said train, an induction generator connected to the opposite end of said train of work elements to be driven thereby, means for electrically connecting said synchronous motor to receive power from said induction generator thereby to exert-a braking torque on .the mill to prevent back-lash between said Work elements and to utilize the braking energy to drive said mill, and means for varying the excitation of said synehronous motor to control the braking torque exerted on the mill by said induction generator.

14. In combination with a rolling mill and means for driving the mill at variable speeds, of a synchronous motor mechanically coupled to the mill driving means whereby the speed of the mill determines the synchronous speed of the motor, and an induction generator mechanically coupled to the mill whereby the generator is always driven by the mill at a predetermined percentage slip speed above the synchronous speed as determined by the frequency developed by the synchronous motor and electrically connected to the motor, thereby to provide for exerting a substantially constant braking torque on the mill over a wide speed range and utilizing the braking energy to drive the mill direct.

' 15. In a rolling mill drive, in combination, a rolling mill having a train of loosely coupled roll stands, a main motor for driving the mill, a source of power for the main motor, a motor of the synchronous type mechanically connected to the main motor whereby a fixedrelation-is maintained between their respective speeds, an induction generator mechanically connected to the end of the train of roll stands and electrically connected to the synchronous motor, said connection being of such character that the induction generator is always driven at a fixed percentage slip above the synchronous speed as determined by the frequency developed by the synchronous motor, and means for varying ehronous motor, thereby to provide for exerting a substantially constant braking torque onthe mill to prevent back-lash between roll stands over a wide speed range as determined by the degree of excitation of the synchronous motor.

16. A regenerative drag system for a machine having a train of work elements and driving means therefor, comprising a wound-rotor induction generator connected to be driven by train of work elements, a synchronous motor mechanically connected in driving relation to the train of work elements and electrically connected to receive power from the wound-rotor induction generator thereby forming a regenerative system, and means for varying the drag torque developed by the regenerative system.

AUGUST L. KRAUSE.

the excitation of the syn- 

